A Novel Chloroplast-Localized Pentatricopeptide Repeat Protein Involved in Splicing Affects Chloroplast Development and Abiotic Stress Response in Rice

Pentatricopeptide repeat (PPR) proteins comprise a large family in higher plants and modulate organellar gene expression by participating in various aspects of organellar RNA metabolism. In rice, the family contains 477 members, and the majority of their functions remain unclear. In this study, we isolated and characterized a rice mutant, white stripe leaf (wsl), which displays chlorotic striations early in development. Map-based cloning revealed that WSL encodes a newly identified rice PPR protein which targets the chloroplasts. In wsl mutants, PEP-dependent plastid gene expression was significantly down-regulated, and plastid rRNAs and translation products accumulate to very low levels. Consistently with the observations, wsl shows a strong defect in the splicing of chloroplast transcript rpl2, resulting in aberrant transcript accumulation and its product reduction in the mutant. The wsl shows enhanced sensitivity to ABA, salinity, and sugar, and it accumulates more H2O2 than wild-type. These results suggest the reduced translation efficiency may affect the response of the mutant to abiotic stress.